A wide variety of capabilities are available, in principle, for the examination of specimens. Particularly popular in this context are, among others, transmission electron microscopy and atomic force microscopy (AFM). One possibility for examining a specimen using an AFM is known, for example, from U.S. Pat. No. 5,253,516. Here the specimen is immobilized in a specimen holder and scanned by a scanning tip. The signals acquired via the scanning tip are electronically converted into an image of the surface of the specimen.
The surface of the specimen is often cut into in order to prepare the surface. Microtomes or ultramicrotomes, for example, can be used for this purpose. These methods, which are known originally from the production of thin sections for TEM examination, can also be successfully used here. It is not necessary, however, to produce thin sections in order to prepare the specimen for AFM examination. The emphasis here, instead, is on preparing the surface of the specimen by way of an exact cut so as to produce a smooth, flat surface. The reason is that specimens to be examined in an AFM must essentially meet two criteria. They must on the one hand have a flat surface which, on the other hand, must be arranged parallel to the surface of a piezoelement on which the sample is mounted. But when a flat surface is produced in a microtome or ultramicrotome and the specimen is removed from the microtome or ultramicrotome mount after cutting, it is practically impossible to arrange that surface once again parallel to the piezoelectric crystal of the AFM.
To circumvent these difficulties, a specimen holder that can be used in a cutting device such as a microtome or ultramicrotome has already been proposed in the article in “Journal of Microscopy” Vol. 195, Pt. 2, August 1999, pp. 161-163. The specimen holder has a central region in which the sample is secured. This central region is removed from the holder of the microtome or ultramicrotome after cutting, and has a flat surface. The central region of the specimen holder is then secured, together with the specimen, on the surface of a specimen stage close to the tip of an AFM. The tip scans the surface of the specimen by means of a piezoelement. Inside the cutting device, the specimen holder is secured with the aid of three screws that must be loosened again for removal of the central insert. In the context of cutting in a refrigeration chamber, which is necessary for many biological or plastic specimens, removal is difficult or impossible. The reason is that the specimen holder must be rotated to the positions of the individual screws. The insert must not fall out when the last screw is loosened, since otherwise the surface could be touched or destroyed. In addition, the insert can be damaged upon removal from a refrigerated chamber, or ambient atmospheric moisture can condense on the surface of the specimen. This, however, renders the sample element unusable for AFM examination.